
where \(\mu _{eX}\)  is the DM-electron reduced mass. The cross section that includes \(g_p\)  is zero due to the odd number of \(\gamma ^ 5\)  in the trace.
So far, in direct detection experiments there is found no evidence of DM-electron elastic scattering. Nevertheless several experiments have set upper bounds on this cross section: XENON1T[1]}, DarkSide50[2]} and SENSEI[3]}. We consider upper bound from the XENON1T experiment to search for DM interacting with electrons[1]}.
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